Police will arrest WikiLeaks founder Julian Assange if he leaves the Ecuadorean Embassy in London, even amid reports that a United Nations’ working group will agree this week that he’s being “arbitrarily detained,” the British government said Thursday.

A U.N. panel will announce in a non-binding decision on Friday that Mr. Assange has been “arbitrarily detained in contravention of international commitments” with respect to the 3½ years he’s spent in the embassy after being granted asylum by Ecuador’s President Correa.

Nevertheless, Britain’s Foreign Office said in a statement on Thursday that it will continue with efforts to apprehend Mr. Assange so that he can be extradited to Sweden to be questioned over allegations of sexual misconduct. He has never been charged with a crime related to the matter.

“We have been consistently clear that Mr. Assange has never been arbitrarily detained by the U.K. but is, in fact, voluntarily avoiding lawful arrest by choosing to remain in the Ecuadorean embassy,” it said in a statement. “An allegation of rape is still outstanding and a European Arrest Warrant in place, so the U.K. continues to have a legal obligation to extradite Mr. Assange to Sweden.”

A spokesman for British Prime Minister David Cameron’s spokesman confirmed to Reuters that authorities will arrest Mr. Assange, 44, if he leaves the embassy.

The WikiLeaks founder said earlier this week that he would surrender to the police on Friday if the U.N. rules against him “as there is no meaningful prospect of further appeal.”

“However, should I prevail and the state parties be found to have acted unlawfully, I expect the immediate return of my passport and the termination of further attempts to arrest me,” Mr. Assange added.

Anna Ekberg, a spokeswoman for the Swedish Foreign Ministry, has since acknowledged that the working group will side with Mr. Assange when it announces the findings of its probe on Friday.

“The working group’s view differs from that of the Swedish authorities. We will forward a reply to the working group tomorrow. It will be more clear tomorrow why we reject the working group’s conclusions,” she told The Guardian on Thursday.

Mr. Assange said previously that he fears he could be brought to the U.S. if he’s extradited from Sweden and tried on charges related to the disclosure of classified documents through WikiLeaks. Pvt. Chelsea Manning, a former U.S. Army intelligence analyst, is currently serving a 35-year prison sentence for supplying WikiLeaks with files pilfered from Pentagon and Department of State databases while deployed.

A lawyer for Mr. Assange told The Associated Press that the hacker-turned-publisher may travel to Ecuador if his passport is returned.